The present invention relates generally to an apparatus for imparting complex rotary motion, particularly for lapping a spherical inner diameter.
Lapping, or the final polishing, of a spherical inner surface has proven to be a difficult and time consuming procedure. A lapping tool composed of a dome grinding section with a rod attached along the central vertical axis of the dome has been used to lap a spherical inner diameter surface. However, to insure all sections of the inner diameter of the sphere are ground equally and that the space inside a workpiece is indeed a sphere, it has been necessary to rotate the workpiece and its holder in a complex pattern to prevent tracking. Tracking is when the lapping tool moves in something other than a random fashion that insures all the areas of the inner sphere surface are polished equally and are the same distance away from the center of the inner spherical volume.
Other machines used in an attempt to induce the sufficiently complex rotary motion to ensure a closer approach to a perfect spherical volume inside the workpiece included an arrangement where an arm pushed around the workpiece in a bowl. Another arrangement included a rotating bin with a floor that moved up and down. While the rotary motion provided to the workpiece was complex in both cases, the time required to lap one spherical surface was long and a substantial amount of noise was generated by the rotating bin with the moveable floor. Thus, a need still existed for an efficient, quick, and quiet method for imparting complex rotary motion for lapping a spherical inner diameter.